U.S. patent application number 10/510888 was filed with the patent office on 2005-09-15 for fuel cell system in the form of a printed circuit board.
This patent application is currently assigned to FRAUNHOFER-GESELLSCHAFT ZUR FORDERUNG DER ANGEWAND. Invention is credited to Burger, Bruno, Hahn, Robert, Hebling, Christopher, Schmitz, Andreas.
Application Number | 20050202297 10/510888 |
Document ID | / |
Family ID | 28685140 |
Filed Date | 2005-09-15 |
United States Patent
Application |
20050202297 |
Kind Code |
A1 |
Schmitz, Andreas ; et
al. |
September 15, 2005 |
Fuel cell system in the form of a printed circuit board
Abstract
The invention relates to a planar fuel cell system comprising at
least two fuel cells which are electrically mounted in series by
means of horizontally overlapping connecting lugs (8 and 8', 18 and
18') and/or strip conductors (40), and a polymer electrolyte
membrane (3). According to the invention, the current path is
guided around the polymer electrolyte membrane, the fuel cell
system is embodied as an arrangement of two printed circuit boards,
according to printed circuit board technique, and the current
collectors and connecting lugs arc embodied as strip conductors of
said printed circuit boards.
Inventors: |
Schmitz, Andreas; (Fuerfeld,
DE) ; Hebling, Christopher; (Freiburg, DE) ;
Hahn, Robert; (Berlin, DE) ; Burger, Bruno;
(Huefingen, DE) |
Correspondence
Address: |
MARSHALL & MELHORN
FOUR SEAGATE, EIGHT FLOOR
TOLEDO
OH
43604
US
|
Assignee: |
FRAUNHOFER-GESELLSCHAFT ZUR
FORDERUNG DER ANGEWAND
Munchen
DE
|
Family ID: |
28685140 |
Appl. No.: |
10/510888 |
Filed: |
May 27, 2005 |
PCT Filed: |
April 11, 2003 |
PCT NO: |
PCT/EP03/03772 |
Current U.S.
Class: |
429/456 ;
427/115; 429/465; 429/483; 429/492; 429/517; 429/535 |
Current CPC
Class: |
H01M 8/0247 20130101;
H01M 8/2432 20160201; H01M 8/1007 20160201; H01M 8/0239 20130101;
H01M 8/241 20130101; Y02P 70/50 20151101; H01M 8/2457 20160201;
H01M 8/0206 20130101; H01M 8/0269 20130101; H01M 8/2465 20130101;
H01M 8/1097 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
429/032 ;
429/034; 429/038; 427/115 |
International
Class: |
H01M 008/10; H01M
008/24 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2002 |
DE |
102 17 034.7 |
Claims
1. A planar fuel cell system comprising at least two fuel cells
which are electrically connected in series in a plane via
horizontally overlapping connecting lugs and in each case on the
anode side and on the cathode side comprise current collectors
which are electrically connected to the connecting lugs, and a
polymer electrolyte membrane, wherein the current path is led
around the polymer electrolyte membrane, wherein the fuel cell
system is designed with a [printed] circuit board technique and as
a composite of a first, anode-side [printed] circuit board and a
second, cathode-side [printed] circuit board, and the current
collectors and connecting lugs are designed as strip conductors of
these [printed] circuit boards.
2. A fuel cell system according to claim 1, wherein the connecting
lugs are located within the boundary of the [printed] circuit board
composite.
3. A fuel cell system according to claim 1, wherein the connecting
lugs in their overlapping region in each case are connected by way
of at least one perpendicular contacting element.
4. A fuel cell system according to claim 3, wherein at least one
perpendicular contacting element is a bore filled with an
electrically conductive material.
5. A fuel cell system according to claim 5, wherein the
electrically conductive material is solder or an electrically
conductive adhesive.
6. A fuel cell system according to claim 4, wherein the bore is
metallised on its inner side.
7. A fuel cell system according to claim 3, wherein at least one
perpendicular contacting element is a rivet.
8. A fuel cell system according to claim 1, wherein gas
distribution structures are incorporated into the first, anode-side
[printed] circuit board.
9. A fuel cell system according to claim 1, wherein gas
distribution structures are incorporated into the second,
cathode-side [printed] circuit board.
10. A fuel cell system according to claim 1, wherein air openings
to the outside are incorporated into the second, cathode-side
[printed] circuit board.
11. A fuel cell system according to claim 1, wherein the fuel cells
in each case have a reaction region which is incorporated into the
[printed] circuit board and which is circumscribed by a raised part
of [printed] circuit board material and/or lacquer.
12. A fuel cell system according to claim 1, wherein the reaction
region contains a gas distribution structure and a current
collector, and a diffusion layer is provided which is deposited
onto the current collector in a flat manner.
13. A fuel cell system according to claim 1, wherein the diffusion
layer is designed as a plastic fabric provided with metallised
segments.
14. A fuel cell system according to claim 1, wherein the strip
conductors and/or the outer contacts contained in the fuel cell
system are coated with single-ply or multi-ply electrically
conductive layers to avoid corrosion.
15. A fuel cell system according to claim 1, wherein the polymer
electrolyte membrane is designed as a segmented membrane electrode
assembly (MEA).
16. A fuel cell system according to claim 1, wherein on the surface
of the [printed] circuit board composite it comprises an electronic
circuit.
17. A fuel cell system according to claim 1, wherein the connecting
lugs of the first and of the second [printed] circuit board are
arranged on these in each case on the reaction region side and are
electrically contacted in a permanent manner by way of a welding
connection.
18. A planar fuel cell system comprising at least two fuel cells
which via strip conductors are electrically connected in series in
a plane and which comprise current collectors electrically
connected to the connection elements, and a polymer electrolyte
membrane, wherein the current path is led around the polymer
electrolyte membrane, wherein the fuel cell system is designed in a
[printed] circuit board technique and as a composite of a first
[printed] circuit board and a second [printed] circuit board, and
the current collectors and connection elements are designed as
strip conductors of these [printed] circuit boards, wherein the
[printed] circuit boards in each case comprise alternating anode
and cathode gas distribution structures and wherein in each case
one adjacent anode current collector and cathode current collector
is electrically connected by way of the connection element.
19. A method for manufacturing a fuel cell system according to
claim 1, wherein a first and a second [printed] circuit board
carrier (substrate) in each case is selected with an upper side and
a lower side, and for both carriers (substrates) on the upper side
in each case the steps of depositing the metallisation onto the
[printed] circuit board carrier (substrate) so that a [printed]
circuit board arises, wherein metal films or thin sheets from a
selection of the materials copper, nickel, gold, titanium or
stainless steel and/or an alloy of these is laminated onto the
[printed] circuit board material, or the metallisation is realized
by way of coating (sputtering, vapour deposition) and a subsequent
galvanic reinforcement of the layer selective etching-away or
milling of the metallisation so that strip conductors arise which
in the reaction region form current collectors and connecting lugs
which in each case border these in a smooth manner incorporating
the gas distribution structures into the [printed] circuit board
depositing the diffusion layers are carried out and subsequently
the membrane-electrode-assembly (MEA) is deposited onto the upper
side of the first [printed] circuit board, the first and the second
[printed] circuit board with their upper sides facing one another
are joined together and the connecting lugs are connected to one
another in a perpendicular manner.
20. A method according to claim 19, wherein as a membrane electrode
assembly (MEA) an MEA catalytically coated over the whole surface
is selected and is segmented before deposition onto the [printed]
circuit board.
21. A method according to claim 20, wherein the segmentation of the
MEA is incorporated by way of laser ablation and/or reactive ion
etching.
22. A method according to claim 19, wherein after the incorporation
of the gas distribution structures, a raised part surrounding the
reaction spaces is deposited so that in each case a recess arises
in the region of the reaction spaces.
Description
[0001] The invention relates to a planar fuel cell system with
which at least two fuel cells are arranged in a plane and are
electrically connected in series via connecting lugs which overlap
horizontally, wherein the current path running the fuel cell system
is led around the polymer electrolyte membrane contained in the
fuel cell system, so that the membrane is not penetrated. The
invention further relates to a method for manufacturing such a fuel
cell system.
[0002] For the addition of the individual voltages of fuel cells
and achieving a higher total voltage which this entails, it is
known to connect several fuel cells electrically in series.
Evidently then, for this, several fuel cells are connected together
in a fuel cell system.
[0003] Usually for this, several fuel cells are arranged above one
another and are pressed together by two end plates by way of screw
connections (stack design). However, with regard to the geometry of
the fuel cell system, a large constructional height and an
unfavourable ratio of the edge length of the fuel cell system
result on account of this design.
[0004] Since, for many applications, it is desirable to realise a
fuel cell system with a significantly flatter geometry, there
exists the need to connect the fuel cells in a fuel cell system in
series in a plane. Here there are various ideas known from the
state of the art:
[0005] The patent document DE 195 02 391 C1 and the PCT published
application document WO 96/18217 disclose so-called "strip membrane
fuel cells" with which the fuel cells are arranged next to one
another and are connected to one another in series. The series
connection is realised here in a manner such that a traverse
conducting structure connects the cathode side of a fuel cell to
the anode side of a further fuel cell and at the same time
penetrates through the membrane contained in the fuel cells. With
this, there exists the disadvantage that leakages may easily occur
due to the passage of the transverse conductor through the
membrane.
[0006] The U.S. Pat. No. 6,127,058 discloses a fuel cell system
with which the fuel cells are arranged in a plane and are connected
in series by way of outer-lying connecting lugs. With this
solution, although the current path does not penetrate the
membrane, the technical manufacturing expense is very active and
prone to breakdown on account of the design, particularly with
regard to the individual large-scale manufacture. Furthermore, it
is considerably disadvantageous that at least two parts to be
assembled individually as current dischargers are required for each
cell.
[0007] In S. J. C Cleghorn et al.: "A printed circuit board
approach to measuring current distribution in a fuel cell", Journal
of Applied Electrochemistry 28 (1998) 663-627, the idea of
measuring the current distribution of a fuel cell by way of using a
fuel cell whose current collector and gas distribution structure
(flow fuel) on the anode side has been realised in a construction
manner of a [printed] circuit board and in a segmented manner is
described. The construction described here however is only suitable
for locally resolved diagnosis purposes in the experimental fuel.
Here too there is no series connection since for these diagnosis
and measurement purposes (current, voltage, impedance spectroscopy)
only individual cell segments are tapped.
[0008] It is the object of the present invention to specify a fuel
cell system which has a low technical expense and may be
manufactured economically in industrial large-scale manufacture,
which is robust in its fuel of application and may be applied in a
manner which is particularly technically simple, which has a flat
geometry and which delivers an increased output voltage with
respect to fuel cells contained in the fuel cell system.
Furthermore, the disadvantages of the mentioned state of the art
are to be avoided.
[0009] It is further the object of the invention to specify a
method for manufacturing such a fuel cell system.
[0010] According to the invention, this object with regard to the
fuel cell system is achieved byway of claim 1 and with regard to
the manufacturing method for such a fuel cell system by way of
claim 17.
[0011] By way of the fact that the fuel cell system is constructed
with [printed] circuit board techniques, one applies reliable
series production manufacturing technology in order to economically
manufacture a fuel cell system with a low electrical output in
large-scale manufacture. This relates also and in particular to the
contacting between the fuel cells which are contained in the fuel
cell system and are connected to one another in series, which are
realised with tried and tested methods of [printed] circuit board
technology.
[0012] By way of the fact that the fuel cell system is designed as
a composite of a first, anode-side [printed] circuit board and of a
second, cathode-side [printed] circuit board, on the one hand the
number of different components which are to be produced during
manufacture of such a system is reduced and thus the manufacturing
is simplified, and on the other hand it is rendered possible to
construct electronic circuits on the [printed] circuit board
composite. These may possibly obtain the energy for the operation
of the circuit from the fuel cell system itself.
[0013] According to the character of the realisation of the fuel
cell system according to the invention in [printed] circuit board
technology, current collectors which are required for the electron
transport in the fuel cell, and connecting lugs via which the fuel
cells contained in the fuel cell systems are connected to one
another in series in a plane, are realised as strip conductors of
the [printed] circuit boards from which the [printed] circuit board
composite is constructed.
[0014] Within the context of this application, a [printed] circuit
board in [printed] circuit board technology indicates a board,
consisting of a [printed] circuit board carrier (substrate) with a
deposited metallisation, wherein usually parts of the metallisation
are removed, e.g. by way of an etching method or by way of milling,
so that the remaining metallisation part forms an electrically
conductive strip conductor. Such metallisations or strip conductors
may be located on the first and/or second side of a [printed]
circuit board.
[0015] By way of the fact that current collectors as well as
connecting lugs are designed as strip conductors, these are
spatially integrated into the fuel cell system in a mechanically
robust and furthermore space-saving manner. Furthermore it is also
advantageously rendered possible to permit the current collector to
merge into the connecting lugs in a smooth manner by way of using
the same metallisation layer for realising the respective strip
conductor.
[0016] Advantageous embodiments of the fuel cell system are
possible according to the dependent claims 2 to 16 and are
explained hereinafter.
[0017] The fuel cell system may advantageously be developed further
to the extent that the connecting lugs are located within the
boundary of the [printed] circuit board composite, thus the
connecting lugs do not project beyond the outline of the [printed]
circuit board composite. The mechanical robustness may thus be
further improved and the expense with regard to technology may be
reduced further with its practical application and with the further
processing.
[0018] If the fuel cell system is advantageously developed further
to the extent that the horizontally overlapping connecting lugs in
their overlapping region in each case are connected by way of at
least one contacting element, the connecting lugs are well defined
with regard to one another and are brought into connection with one
another in a lasting manner and thus the electrical series
connection is realised in a manner in accordance with [printed]
circuit board construction. The contacting element is particularly
advantageous when it is used in combination with the advantageous
further development of the fuel cells in each case having a
reaction region incorporated into the [printed] circuit-board, said
reaction region being bordered by a raised part of [printed]
circuit board material and/or lacquer, since then, on account of
the perpendicular contacting elements, the arising vertical
distance between the overlapping connecting lugs of two fuel cells
contained in the fuel cell system is bridged. The contacting
element may advantageously be realised with a perpendicular design.
It is however not limited to such a design.
[0019] A practical possibility for realising such a perpendicular
contacting element lies in designing it as a bore which is
completely or partly filled with an electrically conductive
material, for example with solder or electrically conductive
adhesive.
[0020] One advantageous further embodiment lies in additionally
leading an electrically conductive linear element (wire, nail or
bolt) through the bore, wherein the electrical contact between the
connecting lug and the conductive, linear element is realised by
way of conductive material filled into the intermediate space lying
therebetween.
[0021] The bore on its inner side may be advantageously metallised,
by which means the contacting is further improved, and the liquid
solder, encouraged by the capillary forces, may flow into the bore.
This may preferably be realised by way of a galvanically grown
metal layer, wherein copper is preferably used.
[0022] It is also possible to design the perpendicular contacting
element without filling with electrically conductive material and
only with the metallisation of the inner side of the bore.
[0023] It is further advantageous to provide several contactings
for each connection of two overlapping connecting lugs, by which
means the respective transition resistance is reduced further. An
alternative, advantageous perpendicular contacting element is a
rivet or press pin which additionally also contributes to the
mechanical strength with respect to the cohesion of the composite
of the [printed] circuit boards.
[0024] The contacting element, given connecting lugs lying directly
on one another, or given an only small distance between these, may
be realised by way of point welding (laser or resistance welding),
wherein the strip conductor at least of one side (cathode-side or
anode-side) must be accessible from the outside for the
welding.
[0025] A further realisation possibility of the contacting element
lies in doing without the bores and filling the intermediate region
of the overlapping connecting lugs with a conductive adhesive or
conductive lacquer. One advantageous further design of this
embodiment lies in incorporating a sheet metal piece or a metal
foil in the intermediate region of the connecting lugs which the
conductive adhesive surrounds.
[0026] Advantageously, gas distributor structures may be
incorporated into the first anode-side [printed] circuit board and
into the second cathode-side [printed] circuit board, wherein the
second, cathode-side [printed ] circuit board additionally or in
place of the gas distributor structures may comprise air openings
to the outside of the fuel cell system.
[0027] If the fuel cells of the fuel cell system in each case
comprise a reaction region incorporated into the [printed] circuit
board, which is bordered by a raised part of [printed] circuit
board material and/or lacquer defining the reaction region, then a
pocket arises on account of this which defines the reaction region
and furthermore renders possible an improved fixation and an
improved assembly of the diffusion layer in the reaction region, as
is provided for in a further advantageous embodiment.
[0028] In this further advantageous embodiment, in the reaction
region in which a diffusion layer is provided, there is also
contained a gas distributor structure and a current collector, and
the diffusion layer is deposited onto the current collector in a
flat manner. The diffusion layer at the same time may be
electrically contacted with the metal layer of the current
collector by way of soldering or an electrically conductive
adhesive, and may also be mechanically fastened.
[0029] The raised part of [printed] circuit board material and/or
lacquer may in a practically particularly advantageous form be an
interconnected frame structure, wherein the applied material may be
plastic, FR4, impregnated paper or similar material which are
laminated on or bonded on, epoxy adhesive which is printed on, or
furthermore solder blocking lacquer.
[0030] The diffusion layer may be a carbon fibre paper or may be
designed in a particularly advantageous manner as a metallised
plastic fabric, and specifically in a manner such that it is the
case of a plastic fabric which preferably only in the region of the
electrodes has metallised segments, e.g. gold (nickel-gold).
Suitable plastic fabrics of polyamide or nylon with diameters of
the threads in the region of 20 and 100 .mu.m and mesh widths of 30
to 500 .mu.m are used as screen-printing fabric. A metallic
segmentation may at the same time be achieved by way of prior
masking or photolithography of the plastic fabric.
[0031] For avoiding corrosion, it is advantageous to provide the
strip conductors consisting for example of copper with single-ply
or multi-ply, electrically conductive and resistant coatings, such
as nickel-gold, Cr or TiW.
[0032] The strip conductors, as also the remaining metallisations,
within the framework of the whole invention, may consist of copper,
nickel, to gold or stainless steel and/or alloys thereof.
[0033] For separating off the anode side from the cathode side in
each case of one reaction space which is realised by a first,
anode-side and an analogously constructed second, cathode-side
[printed] circuit board, for the composite of the two [printed]
circuit boards, a proton-conductive polymer membrane is applied
between these [printed] circuit boards which only has catalytically
coated segments in the region of the reaction spaces of the fuel
cells in the fuel cell system. At the same time, preferably a
segmented membrane electrode assembly (MEA) is used. With this,
this membrane is not penetrated by the current path, i.e. by the
strip-conductor-like current collectors and connecting lugs or by
the perpendicular connection elements which connect the
horizontally overlapping connecting lugs of two fuel cells.
[0034] Hereinafter the advantages of the invention with regard to
the manufacturing method of a fuel cell system according to the
invention are described:
[0035] By way of the fact that a first and a second [printed]
circuit board carrier (substrate) in each case is selected with an
upper side and a lower side and for both carriers (substrates) a
number of equal method steps is carried out in each case on the
upper side, one may reduce the expense for manufacture with
industrial large-scale production. This is accomplished by way of
manufacturing several fuel cell systems from a singe [printed]
circuit board (multiple use).
[0036] By way of the fact that the [printed] circuit board carrier
(substrate) in each case is provided with a metallisation so that a
[printed] circuit board within the context of the present invention
arises, and by way of the fact that this metallisation is
selectively etched away in part regions of the [printed] circuit
board so that strip conductors arise, in a reliable manner capable
of series production, current collectors realised as a strip
conductors and likewise strip-conductor-like connecting lugs which
are contiguous with these in a smooth manner are produced in the
reaction spaces.
[0037] The connecting lugs at the same time do not necessarily have
to be in the same plane as the current collectors, but may also be
realised as a further strip conductor in the form of a
metallisation on the lower side of the strip conductor.
[0038] By way of the fact that gas distributor structures are
incorporated into the [printed] circuit board, the reactands are
led to the reaction space and distributed here. The incorporation
may for example be effected by way of milling, wherein in the case
of a thin strip conductor in the reaction region (for example about
30 .mu.m to 100 .mu.m) one mills through the plane of the strip
conductor in the direction of the [printed] circuit board lower
side, and in the case of a thick strip conductor layer (e.g. 200
.mu.m to 500 .mu.m) one mills or etches into the strip conductor
layer itself.
[0039] By way of the fact that a raised part surrounding the
reaction spaces is deposited, a recess arises in each case in the
region of the reaction spaces, by which means advantageously the
assembly of the diffusion layers is simplified. With this assembly,
an electrical and mechanical connection to the strip conductor
plane and the diffusion layer may be effected by way of soldering
or a conductive adhesive. The assembly may also be encouraged only
by way of a pointwise mechanical connection by way of a
non-conductive adhesive.
[0040] Firstly a first, and a second intermediate product arise in
this manner.
[0041] By way of the fact that subsequently the membrane electrode
assembly (MEA) is deposited onto the upper side of the first
intermediate product and that the first and the second intermediate
product are joined together with their upper sides facing one
another, by way of the MEA, separated anode-side and cathode-side
reaction spaces arise. The joining may be realised by way of
screwing the two plates to one another outside the reaction
regions, and/or bonding then to one another under pressure, by
which means the contact resistance between the strip conductor and
the diffusion layer as well as between the diffusion layer and the
membrane electrode unit is reduced.
[0042] By way of the fact that the connecting lugs of the
anode-side and cathode-side [printed] circuit board are connected
to one another, the electrical series connection of the fuel cells
contained in the fuel cell system is created.
[0043] The present invention is explained hereinafter by way of
several embodiment examples with figures, There are shown in
[0044] FIG. 1 the schematic construction of a fuel cell with
[printed] circuit board technology, in a cross section, which
according to the invention is designed as a composite of two
[printed] circuit boards,
[0045] FIG. 2 the schematic construction of the anode-side
[printed] circuit board, in a plan view,
[0046] FIG. 3 the schematic cross section in the region of the
reaction space and of the MEA of a first embodiment form of a fuel
cell system according to the invention, with three fuel cells,
which are connected in series in a plane,
[0047] FIG. 4 the schematic cross section in the region outside the
membrane electrode assembly (MEA) through a first embodiment of a
fuel cell system according to the invention, with three fuel cells,
which are connected in series in a plane,
[0048] FIG. 5 the schematic upper and lower view of one of the two
[printed] circuit boards shown in FIG. 4, of the [printed] circuit
board composite, without a deposited raised part, diffusion layer
and MEA,
[0049] FIG. 6 the schematic cross section of a second embodiment
form of the fuel cell system according to the invention, with which
three fuel cells in the [printed] circuit board composite are not
only connected electrically in series in a plane via inner-lying
connecting lugs, but also via strip conductors on the surface of
the [printed] circuit board composite,
[0050] FIG. 7 the view of the upper and lower side of one of the
two [printed] circuit boards of the [printed] circuit board
composite in FIG. 6 without the deposited raised part, diffusion
layer and without MEA,
[0051] FIG. 8 the schematic cross section of a third embodiment
form of the fuel cell system according to the invention, with which
in the [printed] circuit board composite three fuel cells are
connected electrically in series in a plane not only by way of
inner lying connecting lugs, but also via strip conductors which
are on the reaction region side and which face one another, on the
respective sides, which face one another, of the anode-side and
cathode-side [printed] circuit board, and which are welded from an
opening accessible to the outside.
[0052] FIG. 9 the view of the upper and lower side of one of the
two [printed] circuit boards of the [printed] circuit board
composite in FIG. 8, without diffusion layer and MEA, but with a
deposited raised part,
[0053] FIG. 10 the schematic cross section in the region of the
reaction space of a fourth, alternative embodiment of the fuel cell
system according to the invention, with four fuel cells whose
anodes and cathodes are arranged alternately on an upper and lower
[printed] circuit board, and are connected in series in a plane by
way of connection of the current collectors of two adjacent anodes
and cathodes by way of a strip conductor.
[0054] FIG. 1 shows a schematic cross section through a fuel cell
with [printed] circuit board technology, which is designed as a
composite of a first, anode-side [printed] circuit board 10 and a
second cathode-side [printed] circuit board 11. The two oppositely
lying [printed] circuit boards 10 and 11, which in this case are
constructed in a completely equal manner and are deposited onto one
another rotated by 180.degree. to one another about the spatial
vertical, in their reaction region are separated by the membrane
electrode assembly (MEA) 3 and are connected to one another at the
edges. The common reaction region formed by the two [printed]
circuit boards 10 and 11 of the [printed] circuit board composite
at the same time consist of the gas distributor structures 6, the
current-collectors 1 and the diffusion layers 2 of both [printed]
circuit boards as well as of the previously mentioned MEA 2 with
the porous catalytic coating 4.
[0055] As may be deduced from the Figure, the gas distributor
structures 6 are incorporated into the [printed] circuit boards 10
and 11 by way of the fact that in each case the upper-lying copper
strip conductor forming the current collector 1 has been
penetrated. Alternatively, with thick copper strip conductors of
about 200 .mu.m to 500 .mu.m it is possible to incorporate the gas
distribution structures into the copper strip conductor itself By
way of this arrangement of the gas distributor structures, the side
of the gas distributor structures which faces the MEA 3 terminals
with the plane of the current collectors 1 in a flush manner. The
diffusion layer 2 is deposited onto this plane over the area so
that the reactands supplied via the distribution structure 6 may
enter into the diffusion layer 2, and so that the diffusion layer 2
is also electrically connected to the current collectors 1.
[0056] The diffusion layer may at the same time consist of
carbon-fibre paper, preferably however also may be designed as a
plastic fabric which in the region of the electrodes 1 has
metallised segments (e.g. gold, nickel gold). Suitable plastic
fabric of polyamide or nylon with diameters of the threads in the
region between 20 .mu.m and 100 .mu.m and mesh widths of between 30
.mu.m and 500 .mu.m are used as screen printing fabric. Although
methods for the permanent metallisation of such fine plastic
fabrics are known, the segment structure may be achieved by way of
a masking or photolithography of the plastic fabric which precede
the metallisation.
[0057] In this example, advantageously the diffusion layer 2 is
electrically contacted and also mechanically fastened to the
current collector 1 by way of soldering or electrically conductive
adhesive. In order to better fix the diffusion layers and to
simplify the assembly of the diffusion layer, the diffusion layers
may be surrounded by a raised part 13 of [printed] circuit board
material, so that in each case a recess (pocket) arises in the part
of the [printed] circuit boards 10 and 11 which forms the reaction
space, and thus a frame structure is formed. This frame structure
is characterised by the distance of the bonding joint 7 to the
plane of the current collector 1 and by nature is located outside
the reaction region. This frame structure may be realised by way of
laminating-on or bonding-on plastic, FR4, impregnated paper or
similar material, by way of printing-on epoxy adhesive,
solder-blocking lacquer or similar means.
[0058] The strip conductors, in all present embodiment examples are
manufactured of copper or the other previously mentioned materials
and within the reaction space of the respective fuel cell, thus
where the strip conductors contact the diffusion layer, serve as
current collectors. Outside the reaction spaces, the strip
conductors are used for discharging the current as well as for
contacting the current discharge contact 5 to the outside of the
fuel cell system, as well as for forming connecting lugs, i.e. for
the electrical series connection of fuel cells in the system. To
avoid corrosion, the copper strip conductor is to be provided with
a single-ply (single-layer) or multi-ply (multi-layer) resistant
coating (e.g. nickel-gold, Cr, TiW).
[0059] The contacts 5 and 5' serve for the external electrical
connection of the fuel cell system and are electrically bonded to
the current collectors 1. Commercially available and standardised
clamp contacts, connecting lugs, pins, rivets etc. may be used as
outer contacts 5 and 5'. In FIG. 1, the attachment of a lateral
outer contact 5 and alternatively to this, the attachment of a
perpendicular outer contact 5' to the outer side of the [printed]
circuit board is represented, which are connected to the strip
conductor by way of soldering or riveting.
[0060] In the case of the use of methanol as a reactant, the outer
side of the anode-side gas distributor is completely or partly
manufactured of a gas permeable membrane or a microstructure with
microscopic openings, which permits carbon-dioxide gas bubbles to
be transported out of the reaction space by way of the
microstructure or to be withdrawn to the outside through the
microscopic openings of the microstructure.
[0061] FIG. 2 shows the anode-side [printed] circuit board 10 of
the fuel cell system of FIG. 1 in a plan view. Recesses of the gas
distribution structure 6 are incorporated into the plane of the
current collector 1 and the [printed] circuit board material lying
thereunder. The membrane electrode assembly is not drawn in this
representation, but its position in indicated by the dashed line
3'. In the present embodiment, the gas distribution structure has a
meandering course. The mechanically deposited raised part 13
forming a frame structure and surrounding the reaction space covers
the current collector 1 in the edge regions. For this reason the
current collector 1 in the plan view may only be recognized in the
region of the reaction space. The current collector 1 covered by
the frame structure is laterally connected to the current discharge
contact 5.
[0062] FIG. 3 shows a fuel cell system with [printed] circuit board
technology which as a composite of an anode-side [printed] circuit
board 10 and a cathode-side [printed] circuit board 11 is basically
constructed analogously to the example shown in FIG. 1. Here three
fuel cells are shown in a plane which are connected electrically in
series outside the region of the membrane electrode unit (MEA) but
within the [printed] circuit board composite.
[0063] Since this figure shows a cross section within the region of
the reaction space, the series connection is not shown in more
detail here.
[0064] The proton-conductive polymer membrane 3 is preferably
designed as a segmented MEA which is segmented in a manner such
that the MEA only has catalytically coated segments 4 in the region
of the reaction spaces of the fuel cell system The segmentation may
at the same time be advantageously incorporated into an MEA which
has been catalytically coated over the whole surface, such as by
way of laser ablation or reactive ion etching (RIE).
[0065] Instead of a cathode-side gas distribution struggle, the
embodiment example has air openings 9 to the outside of the
[printed] circuit board composite. The [printed] circuit boards 10
and 11 are screwed to one another or bonded under pressure, to
reduce the contact resistance at the edge. Connection joints 7
arise.
[0066] The raised parts 13 forming the frame structure here, as
also in the other embodiment examples, circumscribe the reaction
regions.
[0067] FIG. 4 shows a schematic cross section outside the MEA
through a fuel cell system of three fuel cells, with [printed]
circuit board technology. Here a preferred way of electrically
connecting the fuel cells in series in a plane outside the region
of the MEA is represented.
[0068] This is effected in that the copper strip conductor of the
current collector 1 is led into the outside of the reaction region
but permanently in the inside of the boundary of the [printed]
circuit board composite. Thus the connecting lug 8' of the
[printed] circuit board 11 arises. The copper strip conductor of
the fuel cell in the middle in FIG. 3 is likewise led outwards
whilst forming the connecting lug 8. The connecting lugs 8 and 8'
lie opposite one another in the vertical direction, thus overlap in
a horizontal manner. At the same time the connecting lugs 8 and 8'
are connected by way of perpendicular contacting elements 12 for
creating the electrical contact.
[0069] In order not to penetrate the membrane electrode assembly
(MEA) 3, the strip conductor of the current collector 1 is led in
the region outside the polymer membrane or MEA 3 in the form of a
connecting lug 8, into the intermediate space of two adjacent fuel
cell assemblies. A bore 12 is formed through the [printed] circuit
board composite for contacting the oppositely lying strip conductor
lugs 8, 8'.
[0070] The conductive connection in the form of contacting elements
12 between the connecting lugs 8 and 8' arise on account of meting
the inner side of the bore 12. This is preferably realised by way
of a galvanically grown copper layer. In order to further improve
the contacting, the bore maybe completely or partly filled with
solder or conductive adhesive. The contacting may also be realised
without the inner-side metallisation of the bore only by way of the
complete or partial filling of the bore with solder or conductive
adhesive.
[0071] The contacting by way of a contact element 12 in the form of
an electrically conductively filled bore may be advantageously
varied to the extent that before joining together the [printed]
circuit boards 10 and 11, on the reaction-space side, one drills in
each case a bore with a larger diameter so that a larger surface of
the connecting lugs 8 and 8' is released. Then, by way of a bore of
a smaller diameter one creates a continuous bore from the opposite
side, wherein the thinner bore lies coaxially in the thicker bore
and the thinner bore penetrates the connecting lugs 8 and 8'. By
way of filling with solder or conductive adhesive, then, as
previously described, the contacting of the two connecting lugs 8
and 8' to one another may be carried out. On account of the
thicker, first bore, as a whole a larger surface of the connecting
lugs facing one another is released and thus an improved electrical
contacting is achieved.
[0072] The particular preference of this type of contacting by way
of horizontally overlapping connecting lugs 8 and 8' and
perpendicular contacting elements 12 lies in not penetrating the
proton-conductive polymer membrane 3 which in each case on the
anode side and cathode side separates the reaction spaces from one
another.
[0073] If the contacting element 12 instead of a filled bore is
realised by a rivet or press pins, then simultaneously for the
electrical contacting the pressing pressure of the [printed]
circuit board composite is also realised. Furthermore, this
possibility has a very low contact resistance and no temperature
loading on assembly. If the [printed] circuit board material is
removed between a connecting lug 8 and the surface of a [printed]
circuit board 10 or 11 on the reaction region side, then a welding
connection is also possible. For connecting the [printed] circuit
boards 10 and 11, a clamping connection is alternatively or
additionally conceivable.
[0074] FIG. 5 shows the plan view of the surface of the [printed]
circuit board 10, said surface lying on the reaction region side
(II) and lying on the outside (I) in the [printed] circuit board
composite, without a deposited raised part, without diffusion
layers 2 and without MEA 3, wherein the position of the MEA is
indicted by the dashed line 3'.
[0075] On the reaction region side (II), one may clearly recognise
the serpentine structure of the gas distributor structures 6. The
term "gas distributor structures" within the context of this patent
application indicates all distributor structures for distributing
and supplying the reactands in and to the reaction region. At the
same time, the distributor structures or the reactands are not
limited to those which are gaseous. Other forms are just as
conceivable, such as liquid ones, like methanol.
[0076] In the view (II) on the reaction region side, the strip
conductor which surrounds the serpentine gas distribution structure
and forms the current collector 1 may be recognised. This strip
conductor 1 merges smoothly into the connecting lugs 8, in the
drawing in each case on the right at the top and on the right at
the bottom of the reaction region with the gas distribution
structure 6 and the current collector 1. The reaction region whose
boundary in this figure is represented by the rectangle formed by
the gas distribution structure 6 and the current collector 1, lies
in the pocket which circumscribes this reaction region and which is
formed by the raised part of [printed] circuit board material which
is not shown in more detail in this figure. The gas distribution
structure at the same time penetrates this raised part forming the
pocket at the location where two fuel cells are connected to one
another with regard to the supply of reactands.
[0077] The perpendicular contacting elements 12 are also shown in
the figure, from the view (I) lying at the outside as well as from
a view from the reaction region side (11) wherein in the latter
view the penetration of the perpendicular connection elements is
represented by the connecting lugs 8.
[0078] It is to be clearly seen that the electrical circuiting by
way of the connecting lugs 8 takes place outside the reaction
region but within the outer boundary of the [printed] circuit board
10. By way of this one not only achieves the advantage that on
account of the electrical contacting, the MEA 3' indicated only in
its position in this figure is not penetrated and by way of this
leakages may not arise, but also the usually high electrical losses
in a planar arrangement of series connected fuel cells is avoided
by way of the fact that the current through the preferably used
well-conducting copper strip conductors which are formed by the
current collectors 1 and the connecting lugs 8 is discharged to the
edge.
[0079] The FIGS. 6 and 7 show a second embodiment. Here the
inner-lying connecting lugs 14 and 14' of the [printed] circuit
boards 10 and 11 are shown similarly to that in FIGS. 4 and 5, but
the inner-lying connecting lugs 14 and 14' (see FIG. 7) only form
an extension of the current collectors to the outer region and no
longer have the lateral extension bent at an angle, in the
direction of the adjacent fuel cell of the connecting lugs 8 and 8'
of FIGS. 4 and 5.
[0080] The particularity of this variant of the electrical
circuiting of the fuel cells in series in a plane lies in the fact
that by way of inner-lying connecting lugs 14 and 14', in each case
at least one electrical connection 15 to the outer-lying contacts
40 is created, wherein the outer-lying strip conductors 40 are
arranged such that --analogously to the connecting lugs 8 and
8'--the outer lying circuiting strip conductors 40 in each case of
two fuel cells overlap as shown in FIG. 6 and are connected to one
another by way of one or more perpendicular contacting elements 16.
The basic integral homogeneity of the inner-lying connecting lugs
14 and the outer lying strip conductors for circuiting 40 becomes
particularly evident from FIG. 7. In this embodiment form the
inner-lying connecting lugs 14 as well as the outer-lying strip
conductors 40 are electrically contacted for the series connection,
wherein the electrical connection is realised in principle in the
same manner as in the FIGS. 4 and 5.
[0081] FIGS. 8 and 9 show a third embodiment form. Here the
inner-lying connecting lugs 17 and 17' of the [printed] circuit
boards 10 and 11, in each case by way of a perpendicular contacting
element 19, are electrically connected to the strip conductors 18
and 18' of the anode-side and cathode-side [printed] circuit board,
said strip conductors facing one another. The strip conductors 18
and 18' which on the reaction region side face one another, thus
lie opposite one another, only have a slight distance to one
another or form a border surface. By way of the bore, the
inner-side strip conductors 18 and 18' lying opposite one another,
at a location at which this strip conductors lie opposite one
another, are accessible from the outside and may be permanently
electrically contacted by way of point welding or laser
welding.
[0082] FIG. 10 shows the cross section through the reaction space
of a further embodiment, wherein anode gas distributor structures
24 and cathode gas distributor structures 23 are arranged in an
alternating manner on each of the [printed] circuit boards 21 and
22, wherein the current collector 1' of the cathode gas distributor
is electrically connected to the adjacent current collector 1 of
the anode gas distributor via a strip conductor 25.
[0083] In this example, the cathode gas distribution structure 23
is represented with air openings to the outside of the fuel cell
system. Instead of air openings, one may also use a closed gas
distribution structure 24 such as that of the anode gas distributor
24.
[0084] The particular preference of this embodiment lies in the
fact that by way of the alternating arrangement of the anode-sides
and cathode-sides of the fuel cells, one may do without a
contacting of the one side onto the other side of the [printed]
circuit board composite. The fuel cell in the [printed] circuit
board composite may thus be realised merely by way of bringing the
two [printed] circuit boards 21 and 22 onto one another, which is
not so trick with regard to design, and is inexpensive to
manufacture.
[0085] A fuel cell system according to the invention, with a height
of 2 mm to 3 mm has only a very low constructional height. Due to
the flat geometry of such a fuel cell system it is particularly
suitable for integration into the outer housing of an apparatus. In
particular with the construction manner with a cathode which is
open to the outside or corresponding openings to the outside for
the supply of air, one may operate such a fuel cell system in a
self-breathing and passive manner without having to convectively
supply oxygen such as by way of a ventilator.
[0086] With [printed] circuit board technology, it is possible to
provide a manufacturing technique which is compatible with series
production and is reliable for manufacturing fuel cell systems with
a relative low electrical output in large batch numbers in an
inexpensive and technically less complicated manner. In particular,
the electrical series connection, i.e. the contacting of fuel cell
to fuel cell of the fuel cell system may be realised by way of a
tried and tested industrial method.
[0087] It is furthermore very advantageous that due to the design
as a [printed] circuit board composite, electronic circuits may be
constructed on the fuel cell system in a simpler manner. Such
circuits on the one hand may detect, control or improve the
behaviour of the fuel cell system and on the other hand however the
consumer to be supplied may also be deposited directly onto the
[printed] circuit board composite. As examples of the first
mentioned electronic circuits the following are to be named:
electronics for DC-DC conversion, electronics which may be equipped
with sensors, for measuring and detecting operating parameters of
individual fuel cells (current, voltage, impedance, temperature
etc.) electronics for controlling the flows of reactands
(activation of microvalves or micropumps), electronics for the
protection of individual fuel cells by way of protective or bypass
diodes, or electronics for bridging individual fuel cells which are
no longer capable of functioning.
[0088] One example of a consumer to be supplied directly on the
[printed] circuit board in the form of a microelectronic circuit is
e.g. a sensor which is supplied electrically in a direct manner by
way of the fuel cell system.
* * * * *